In the last several years, there has been a trend in the industry to produce products which are both of a higher quality and environmentally friendly. This is especially true in the automotive industry wherein both consumer groups and environmental organizations have pushed for safer, higher-quality vehicles that are more fuel efficient and less detrimental to the environment. Recycling old vehicles has been one answer to resolving the environmental issues associated with vehicles which have run out their useful life. Automotive salvage markets have developed for these vehicles. The vehicles are partially dismantled and sold as scrap metal wherein the metal is melted down and reformed into various parts. Because of the environmentally-unfriendly nature of lead, the gasoline tanks of vehicles must be removed prior to the recycling of the vehicle. Gasoline tanks are commonly made of carbon or stainless steel coated with a terne coating containing 80% or more lead. As a result, these terne coated gas tanks must be disposed of in dumping yards or landfills. Not only does the terne coated gasoline tank take up space in the landfills, but there is a concern, though unfounded, with the lead leaching from the terne coating into the landfill site and potentially contaminating the surrounding area and underground water reservoirs. The terne coating on the gasoline tank was originally applied to protect the stainless steel or carbon steel tank from corroding. However, the corrosion resistance provided by the terne coating is commonly defective due to the limited coating thickness and coating processes. Standard terne coated gasoline tanks are coated with a 6-8 lb. terne coating (0.0003-0.0004 inch), which is a very thin coating resulting in pinholes in the coating (small uncoated areas on the gasoline tank surface). Due to the thin layer of the terne coating and the pinholes, the coating on the metal sheet, upon being drawn by a die into a gasoline tank component, had a tendency to tear or shear thereby exposing the metal surface. Furthermore, the pinholes in the coating are enlarged as the coated sheet is drawn thereby further exposing more of the metal surface. These exposed surfaces, subjected to the direct environment, readily begin to corrode and over time compromise the structural integrity and safety of the gasoline tank and may ultimately result in the leaking of the gasoline from the tank. The non-uniform coating of the gasoline tank with the terne coating is especially evident when stainless steel is used since terne does not bond as well to the stainless steel as compared to carbon steel.
Metallic coatings such as tin or zinc have been tested as substitutes for terne coatings with limited success. The electroplating of tin or zinc onto metal sheets to be formed into gasoline tanks has not proved to be a reliable and cost effective substitute for terne coatings. Electroplating of tin or zinc forms coating thicknesses which are much thinner than hot-dipped terne coatings thereby making electroplated coatings much more susceptible to tearing or shearing when the electroplated sheet is drawn on a die. Electroplating is also much more expensive and time consuming than a hot-dipped terne process.
Plastic gasoline tanks have been used but with limited success. Although the use of plastic tanks eliminates the environmental concerns associated with lead, the plastic in-of-itself is a non-environmentally-friendly compound which does not readily degrade and therefore must be disposed of in a landfill. The plastic used to make the gasoline tanks is usually not the type that can be recycled. Plastics have also been found to be less reliable than metal gasoline tanks. Specifically, plastic gasoline tanks have a tendency to rupture upon impact, such as from a car accident, whereas a metallic gasoline tank would absorb much of the shock by bending and slightly deforming. Furthermore, the plastic tanks are more susceptible to being punctured from roadside debris since the plastic skin is not as strong or malleable as the skin of a metallic gasoline tank. Plastic gasoline tanks also require new materials, special tools and new assembly methods to fix and install the tanks due to the nature of plastic and its physical properties. These additional costs and shortcomings of plastic tanks have resulted in very little adoption of plastic tanks in present day motor vehicles. Due to the environmental concerns and problems associated with terne coated gasoline tanks and with the shortcomings of plastic gasoline tanks, there has been a demand for a corrosive-resistant, environmentally-safe gas tank which can be easily and safely installed into a vehicle without requiring additional tools and assembly methods and can be subsequently recycled with a vehicle once the useful life of the vehicle has ended.